The disclosure relates to suspension plasma spray. More particularly, the disclosure relates to suspension plasma spray feeder apparatus.
Suspension plasma spray (SPS) is a form of plasma spray wherein a particulate suspended in a carrier liquid is delivered to the plasma spray gun. This may be distinguished, for example, from other systems wherein powder is fed directly into the gun to interact with plasma and any residual carrier gas or from non-powder systems (e.g., wire systems). Suspension plasma spray systems present issues of clogging not relevant to other spray systems. It has been known to use an orifice in the flowpath to control out feed rate and pressure of the output. Filters may be employed to prohibit large agglomerates or particles from building up in the flow path or reaching an orifice.
In some examples, a recirculating flowpath is used to prevent clogging when the gun is not spraying. For example, a valve is provided in a suspension supply line somewhere between a suspension source and the gun. The valve may shut off suspension flow to the gun. To prevent blockage upstream of the valve, a return line/flowpath is provided branching from the supply line/flowpath to the source just upstream of the valve. This return flowpath may have its own valve or, equivalently, the first valve may be a three-way valve. Thus, when the flow to the gun is shut off, flow along the branch flowpath is opened and flow can recirculate to avoid clogging. The branch flowpath may contain an orifice for providing a sufficient pressure restriction to limit the flow rate of the recirculating flow.